Flexural hybrid span beam

Abstract

A method for producing a flexural hybrid span beam includes casting a first layer of ultra-high performance concrete (UIHPC) into a bottom of a mold, the first layer comprising steel fibers that are randomly oriented and dispersed. The method includes self-curing the first layer for at least 48 hours to form an unfinished top surface of the first layer. The method includes casting a second layer of plain concrete, over the unfinished top surface of the first layer, in the mold, wherein the second layer of plain concrete is not reinforced by steel bars. The method includes curing the first layer and the second layer to form the flexural hybrid span beam. An interface between the first layer and the second layer is substantially flat and has a periphery conforming to a shape of the mold.

1 . A method for producing a flexural hybrid span beam, the method comprising:
 casting a first layer of ultra-high performance concrete (UHPC) into a bottom of a mold, the first layer comprising steel fibers that are randomly oriented and dispersed;   self-curing the first layer for at least 48 hours to form an unfinished top surface of the first layer;   casting a second layer of a plain concrete, over the unfinished top surface of the first layer, in the mold, wherein the second layer of the plain concrete is not reinforced by steel bars;   curing the first layer and the second layer to form the flexural hybrid span beam; and   removing the flexural hybrid span beam from the mold,   wherein an interface between the first layer and the second layer is substantially flat and has a periphery conforming to a cross-sectional shape of the mold, and wherein the first layer is the bottom layer of the flexural hybrid span beam and the second layer is the top layer of the flexural hybrid span beam.   
     
     
         2 . The method of  claim 1 , wherein the second layer is cast over the unfinished top surface of the first layer after self-curing the first layer for the at least 48 hours. 
     
     
         3 . The method of  claim 1 , wherein the first layer and the second layer are cured for about 28 days to form the flexural hybrid span beamflexural hybrid span beam. 
     
     
         4 . The method of  claim 1 , wherein the steel fibers are coated by copper. 
     
     
         5 . The method of  claim 4 , wherein the steel fibers are straight and have an average diameter of about 0.2 mm. 
     
     
         6 . The method of  claim 5 , wherein the steel fibers have an aspect ratio of about 65 and a maximum tensile strength of 2500 MPa. 
     
     
         7 . The method of  claim 1 , wherein the first layer of UHPC further comprises a type 1 ordinary Portland cement (OPC), a micro silica, a fine aggregate, a superplasticizer, and water. 
     
     
         8 . The method of  claim 7 , wherein the first layer of UHPC consists of at least one type 1 OPC, at least one micro silica, at least one fine aggregate, at least one superplasticizer, the water and the steel fibers. 
     
     
         9 . The method of  claim 8 , further comprising;
 mixing the at least one type 1 OPC, the at least one micro silica and the at least one fine aggregate;   then adding the water and the at least one superplasticizer; and   then adding the steel fibers to form the UHPC.   
     
     
         10 . The method of  claim 7 , wherein the first layer of UHPC has a width of 120-180 mm, a length of 760-1200 mm, a thickness of 20-50 mm, a compressive strength of at least 160 MPa, and a tensile strength of about 30 MPa. 
     
     
         11 . The method of  claim 1 , wherein the second layer of the plain concrete comprises a type 1 OPC, a fine aggregate, a coarse aggregate, and water. 
     
     
         12 . The method of  claim 11 , wherein the second layer of the plain concrete consists of at least one type 1 OPC, at least one fine aggregate, at least one coarse aggregate, and the water. 
     
     
         13 . The method of  claim 12 , further comprising;
 mixing the at least one type 1 OPC, the at least one fine aggregate and at least one coarse aggregate; and   then adding the water to form the plain concrete.   
     
     
         14 . The method of  claim 11 , wherein:
 the fine aggregate has an average size of about 0.6 mm, and   the coarse aggregate has an average size of 10-20 mm.   
     
     
         15 . The method of  claim 11 , wherein a ratio of the water to the type 1 OPC is about 0.42, and the second layer of plain concrete has a width of 100-180 mm, a length of 760-1200 mm, and a thickness of 110-150 mm. 
     
     
         16 . The method of  claim 1 , wherein;
 the unfinished top surface of the first layer is substantially flat, and   the second layer is cast completely above the unfinished top surface of the first layer.   
     
     
         17 . The method of  claim 16 , further comprising;
 before the self-curing, treating the first layer with a trowel; and   before the curing, treating the second layer with the trowel.   
     
     
         18 . The method of  claim 1 , wherein;
 the first layer has a first thickness of 20-50 mm; and   the second layer has a second thickness of 110-175 mm.   
     
     
         19 . The method of  claim 1 , wherein:
 the first layer has a first width of 150 mm, a first length of 900 mm and a first thickness of 50 mm,   the second layer has a second width of 150 mm, a second length of 900 mm, and a second thickness of 150 mm, and   the flexural hybrid span beam has a failure load of 34,000 newtons and a deflection at a flexural failure load of 1.28 mm.   
     
     
         20 . The method of  claim 1 , wherein the flexural hybrid span beam consists of the first layer and the second layer.